I'm using Ruby 1.8.6 btw.
For the longest time today (it seems) I've been trying to understand exactly the operating difference between class_eval and instance_eval. There are some obvious differences I'm perfectly aware of (e.g. class_eval is only on Class objects), but the reality is that some irb tinkering has left me more confused than ever. Given the following:
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class Foo
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# could be any class
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end
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f = Foo.new
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# Try out instance eval on f's class (Foo)
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f.class.instance_eval do
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define_method :made_by_inst_eval do
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puts "This method was made by calling instance_eval"
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puts "Current 'self': #{self}"
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puts "Current class of 'self': #{self.class}"
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end
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end
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f.made_by_inst_eval
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Gives me this:
- This method was made by calling instance_eval
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Current 'self': #<Foo:0x8f098>
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Current class of 'self': Foo
If I then try doing the exact same thing with class_eval instead:
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f.class.class_eval do
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define_method :made_with_class_eval do
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puts "This method was made by calling class_eval"
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puts "Current 'self': #{self}"
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puts "Current class of 'self': #{self.class}"
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end
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end
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f.made_with_class_eval
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I then get the same damn result:
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This method was made by calling class_eval
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Current 'self': #<Foo:0x8ec88>
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Current class of 'self': Foo
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So, what's the difference between these two calls? In this particular situation? In general?
Some clear thoughts would be ever so appreciated!
